> ## Documentation Index
> Fetch the complete documentation index at: https://diameterpay.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Diameter API: Banking Infrastructure for Fintechs

> Diameter API gives fintechs a single REST API to onboard users, open virtual accounts, and process domestic and international wire payments.

Diameter is a banking infrastructure API that sits between your fintech product and partner banks, giving you a single, unified REST interface to handle the full lifecycle of end-user onboarding, virtual account management, and payment processing — without requiring a direct integration with each bank.

## What Diameter Solves

Building compliant, bank-connected financial products is slow and expensive. Every bank speaks a different protocol, enforces different onboarding rules, and surfaces payments through a different API. Diameter abstracts all of that away. You integrate once and gain access to multiple partner banks and payment rails through a consistent set of endpoints and data models.

> [card] [Quickstart](https://diameterpay.mintlify.site/quickstart.md)
>
> Obtain credentials, create your first end user, and fire a wire payment in under 15 minutes.

> [card] [Authentication](https://diameterpay.mintlify.site/authentication.md)
>
> Learn how OAuth2 Client Credentials work, which scopes to request, and how to handle token expiry.

> [card] [Core Concepts](https://diameterpay.mintlify.site/concepts/tenants-and-products.md)
>
> Understand Tenants, Products, End Users, Accounts, and Payments before you write your first request.

> [card] [API Reference](https://diameterpay.mintlify.site/api-reference)
>
> Browse every endpoint, request schema, and response model in the full OpenAPI reference.

## Key Capabilities

> [card] End-User Onboarding
>
> Create individual and business end users, submit KYC identity data, and enroll them in one or more bank products in a single API call.

> [card] Virtual Accounts
>
> Open segregated virtual accounts for each end user, query balances, and retrieve bank-assigned account numbers — all without touching the bank's portal.

> [card] Domestic Wire Payments
>
> Initiate ACH-like domestic wire transfers between virtual accounts or to external beneficiaries using simple debit/credit instructions.

> [card] International Wire Payments
>
> Send cross-border payments in USD with support for SWIFT intermediary routing and correspondent bank details.

> [card] Internal Transfers
>
> Move funds between accounts within the same Diameter tenant instantly, with no external payment rail involved.

> [card] Webhooks
>
> Subscribe to real-time event notifications for account status changes, payment completions, and onboarding outcomes.

## Partner Banks

Diameter currently operates through two partner banks. When you create a **Product** (see below), you choose which bank backs it.

| Partner Bank | Region | Supported Rails |
| - | - | - |
| **Portage Bank** | United States | Domestic wire, internal transfer |
| **Slovak Savings Bank** | European Union | SEPA, international wire (SWIFT) |

> [!NOTE]
>
> Partner bank availability depends on your tenant's approved product configuration. Contact [support@diameterpay.com](mailto:support@diameterpay.com) to enable a specific bank or rail.

## Tenant and Product Model

Understanding the two-level organizational model is essential before making your first API call.

**Tenant**
Your organization is represented as a *Tenant* in Diameter. All API credentials, Products, End Users, and Accounts belong to your Tenant. When you call `GET /v1/tenants/self` you retrieve your Tenant's configuration, approved products, and feature flags.

**Product**
A *Product* is a specific bank integration tied to your Tenant. Each Product maps to a single partner bank and defines the account type, currency, and compliance rules that apply to end users enrolled in it. Diameter supports two product models:

| Product Type | Description |
| - | - |
| **Proprietary** | Your Tenant owns the banking relationship directly. End-user accounts appear under your legal entity. |
| **Fiduciary** | Diameter or a licensed partner holds the banking relationship on your behalf. Suitable for fintechs without a direct bank agreement. |

When you onboard an end user you supply a `productId` to indicate which Product — and therefore which bank — the user should be enrolled in.

## API Versioning

The current stable version of the Diameter API is **0.11.7**. All endpoints are prefixed with `/v1/`. Breaking changes will be released under a new major version prefix (e.g., `/v2/`) with a documented migration path and a deprecation window of at least 90 days.

Include the `x-idempotency-key` header on all write requests to ensure safe retries. See the [Quickstart](https://diameterpay.mintlify.site/quickstart.md) for details.

## Getting Help

If you have questions about credentials, product configuration, compliance requirements, or anything else, reach out to the Diameter team:

**Email:** [support@diameterpay.com](mailto:support@diameterpay.com)

The support team typically responds within one business day. For urgent production issues, mark your email subject line with `[URGENT]`.


This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.